1. Field of the Invention
The present invention relates to document feeders such as a printer or printing machine that sequentially separate stacked sheets into single sheets for conveyance, and more particularly to document feeders such as inserters and the like that collate sheets printed at an image-forming apparatus or the like and insert cover sheets for a bookbinding process, and accurately separate and convey special sheets such as those having a window opening therein.
2. Description of the Related Art
Generally, a variety of apparatuses that consecutively print sheets, such as printing machines, copiers or so-called printing systems are recently being used as on-demand printing systems. In such printing systems, not only are sheets printed using a predetermined printing process and discharged, but also finishers are widely used to sort discharged sheets into a predetermined number of sheets, align them, and then implement a predetermined finishing process thereto, such as stapling or gluing or the like. There are cases in which a cover sheet or a partitioning sheet must be inserted, depending on the process at the finisher, such as partitioning or collating. Therefore, an inserter is disposed between the image-forming apparatus and the finisher linked thereto to insert cover sheets or partitioning sheets to a predetermined order position of sheets sequentially conveyed out from the image-forming apparatus. Thereafter, the series of sheets are bound or collated.
The types of sheets handled by that kind of inserter can be a thick sheet such as a cover sheet, or a thin sheet, such as traditional Japanese paper. It could also be coated sheets, such as glossy paper, or OHP sheets that are also in wide use. Thus, a paper feeder that precisely feeds one sheet at a time from a stacker is in demand. This kind of conventional paper feeder that is provided a vacuum pick-up for vacuuming an edge of a stacker to pull out single sheets is known as a printing system. Paper feeders equipped with this kind of vacuum pick-up are able to separate and feed a wide variety of sheets comparatively accurately, but they are large and require space for installation. They are also expensive.
On the other hand, different types of office equipment, such as copiers, printers or facsimile machines are well known feeding apparatuses that use feeding rollers to touch sheets, kick out sheets stacked on a stacker, and to separate the sheets into single a sheet for feeding (along with a separation member such as a friction pad or separating rollers (retard rollers)). Also, downstream of the feeding rollers, conveyance means are provided to receive and convey sheets to a processing position. For example, a pair of rollers is arranged in a sheet conveyance guide downstream of the feeding rollers. These are registration rollers. They are stopped when the leading edge of the sheet is fed from the feeding rollers. That action causes the sheet to bend and that enables the leading edge of the sheet to become properly aligned (to remove any skewing). This registration roller mechanism that feeds sheets toward the processing position is widely known.
A separation mechanism using friction described above is composed of one feeding roller arranged in the center of the width direction of a sheet and a separation member (reverse rotating roller or pad or the like) that is in contact thereto. The feeding roller kicks out the sheet, but the separation pad inhibits the double-feed of sheets. To prevent a double-feed or non-feed with such a structure for separation, the feeding roller and separation member are composed of materials providing a high coefficient of friction. Increasing the contact pressure therebetween is widely known, but examples have not conventionally been provided. Nevertheless, separation devices are widely known.
However, if the coefficient of friction and contact pressure are high, ordinary paper (particularly thin sheets) can become wrinkled or box-eared which damages the sheet. The friction between the feeding rollers and the friction member can become too high which increases the frequency to replace parts. When feeding sheets toward the processing position with this registration mechanism, the feeding rollers are stopped so that subsequent sheets are not fed and the registration rollers pull the sheet to convey it. At that time, if there is a high coefficient of friction between the feeding rollers and the separation member, the conveyance load will be increased which causes the problem of having to vary the load according to the type of sheet.
A wide range of sheet types are used as cover sheets. This includes special sheets such as windowed sheets formed with notched openings for a title. To stack and store sheets so that an edge of the notched window and the leading edge of the next sheet do not catch each other when windowed sheets to be discharged are stacked vertically, a jump member that projects upward from the tray support surface is provided in a tray structure for handling windowed sheets. Sheets sequentially advancing are caused to jump by an oblique surface provided on the jump member. (See Unexamined Japanese Pat. Pub. 2006-82901.)
However, if windowed sheets are stacked in tray means and sequentially fed downstream starting from the uppermost sheet, the edge of the notched opening of the sheet can get caught on the notched opening of a lower sheet which leads to a non-feed or a double-feed. A method for manually feeding single special sheets from a manual feed inlet has been adopted, but that is not appropriate for an apparatus that operates continually.
Thus, the inventors analyzed the behavior of sheets when windowed sheets formed with window openings such as for titles, and the like, are separated and conveyed. They discovered that the opening edge of the trailing side gets caught on the leading edge of the of a lower sheet when the uppermost sheet is kicked out and fed along the lower sheet which causes a double-feed. It was also learned that a double-feed or a non-feed happens more easily when upper and lower sheets have been pressed closely to be cut to form the window in this kind of windowed sheet.
The present invention provides a paper feeder that securely separate and feed windowed sheets with notched openings stacked on a tray sequentially from the uppermost sheet. Furthermore, the present invention provides a paper feeder that securely separates and feeds either windowed sheets or ordinary sheets to a downstream processing position and bookbinding apparatus equipped with the same.